1. Field of Invention
The present invention relates to an image sensor device and a method for making the image sensor device.
2. Description of Related Art
As shown in FIG. 1, typically, an image sensor device includes optical pixels 100 and an electronic circuit 200, wherein the electronic circuit 200 is made by a CMOS process in most nowadays applications. FIGS. 2A-2D show, by way of cross section diagrams, the steps for making a pixel:
Referring to FIG. 2A, an image sensor area 12 is formed in a substrate 11; and an oxide layer 13a, a polysilicon layer 13b, and multiple dielectric layers 14 are formed thereabove respectively. To match with the CMOS process, the oxide layer 13a and the polysilicon layer 13b are preferably made of materials the same as the gate dielectric layer and the gate conductive layer for making the electronic circuit.
Referring to FIG. 2B, with the polysilicon layer 13b serving as an etch stop layer, an etch process is taken to etch the dielectric layers 14, forming a light passage 15 above the image sensor area 12. The light passage 15 helps to let more light pass through and reach the image sensor area 12.
Referring to FIG. 2C, because the polysilicon layer 13b is non-transparent, to increase the light sensitivity of the image sensor area 12, the polysilicon layer 13b is removed. However, this etching process may damage the surface of the image sensor area 12, degrading the image sensing capability and accuracy of the device.
Referring to FIG. 2D, after the polysilicon layer 13b is removed, a passivation layer 16 is provided to cover an upper part of the topmost dielectric layer 14; next, a color filter layer 17 is formed above the passivation layer 16, and thereafter a micro-lens layer 18 is formed above the color filter layer 17.
With respect to the light passage and the CMOS image sensor, U.S. Pat. Nos. 6,861,686; 6,792,804; 7,205,623; 7,400,003; 7,462,507; 7,193,289; and U.S. publication No. 2007/0262366 disclose relevant technical details.
In FIGS. 2A-2D and the foregoing prior art citations, there is a drawback that multiple etching processes damage the surface of the image sensor area 12, degrading the image sensing capability and accuracy of the device.